Electric wave reception



June 1, 1937. BEERS ELECTRIC WAVE.RECEPTION Filed April 16, 1928 3 Sheets-Sheet l INVENTOR 69076.4. Bea/5.

. June 1, 1937. G. L. BEERS ELECTRIC WAVE RECEPTION Filed April 16, 1928 5 Sheets-Sheet 2 INVENTOR 350g? L Bee/:5

ATTORNEY June 1, 1937. BEERS 2,082,478

ELECTRIC WAVE RECEPTION Filed April 16, 1928 s Sheets-Sheet 3 WITNESSES: I INVENTOR I Georg-645x 5 422 BY f ATTORNE fatented June 1, 1937 UNITED STATES tATENT OFFICE ELECTRIC WAVE RECEPTION Application April 16, 1928, Serial No. 270,285

21 Claims.

My invention relates to electric wave reception and it has particular relation to the reception and amplification of electric waves at radio-frequencies.

Although certain phases of my invention are capable of broad application to radio receiving systems of many types, the invention, considered as an entity, may be regarded as primarily directed toward improving superheterodyne receiving systems of the type disclosed in the patent to Armstrong, 1,342,885.

One object of my invention is to provide a superheterodyne receiving system that shall have improved selectivity characteristics.

Another object of my invention is to provide a superheterodyne receiving system in which the so-called image-frequency response shall be minimized.

Another object of my invention is to provide a superheterodyne receiving system that shall be substantially incapable of radiating the locally generated oscillations.

Another object of my invention is to provide, in a superheterodyne receiving system of the unicontrol type, means whereby the tuning of the os cillator stage shall be unaffected by changing the thermionic tube comprised therein.

Another object of my invention is to provide, in a radio receiving system of the aforementioned type, improved inter-tube coupling transformers between the thermionic tubes comprised in the intermediate-frequency amplifier.

Another object of my invention is to provide, in a superheterodyne receiving system, improved means for securing the proper frequency relation between the tuning of the oscillation generator and the tuning of the radio-frequency amplifying stages.

Another object of my invention is to provide an improved circuit network for so inter-connecting a plurality of thermionic devices comprised in a radio receiving system to a source of anode potential therefor that variations in said anode-potential source shall be substantially ineffective to cause variations in the output from said receiving system. 7

Another object of my invention is to provide an improved circuit network of the aforesaid type that shall comprise means for deriving a plurality of gridbiasing potentials from the anode-potential source.

Another object of my invention is to provide an efficient volume-control device for a radio receiving system.

A superheterodyne receiving system, constructed and arranged according to a preferred embodiment of my invention, comprises a plurality of thermionic devices of the equipotential-cathode type interconnected in cascade through tuned coupling-transformers and supplied with anode potentials and grid-biasing potentials from a rectifying device that may be energized from any convenient source of alternating current. The first amplifying tube of the series is arranged to be coupled to an energy-collecting device through a substantially non-inductive resistor of sufilcient magnitude to prevent the antenna from radiating energy from the local oscillator. The resistor does not affect the sensitivity of the system.

The thermionic devices comprised in the intermediate-frequency amplifying stages are coupled together through tuned transformers of a novel type. Considered from an electrical standpoint, the intermediate-frequency transformers are so proportioned that they are somewhat analogous to band-pass filters; considered from a. mechanical standpoint, they are so mounted in individual shielding devices, and so provided with tuning condensers having easily accessible adjusting elements that they may be accurately calibrated and tuned before being mounted in a complete receiver, with complete assurance that the precalibration will not later be changed.

Volume-control is accomplished by varying the grid-biasing potential applied to all of the highfrequency amplifying tubes, such potential being derived from the anode-potential supply through a resistor-network, and the various thermionic tubes comprised in the entire receiving system are so grouped with respect to the said network that a variation of the biasing potential applied to the said high frequency tubes does not greatly disturb the potential applied to the remaining tubes.

I find it preferable to connect all of the main tuning condensers together for simultaneous control, and it is accordingly necessary that the frequency of the oscillations generated by the local oscillator shall not be affected when different thermionic tubes of the same type are substituted therein. I provide for this condition by coupling the frequency-determining circuit of the local oscillator, in which is included one of the said main tuning condensers, very loosely to the grid and cathode of the oscillator tube, in order that the grid-cathode capacity of the tube shall be negligible in fixing the frequency to which the said circuit is resonant.

In addition, I have provided a novel arrangement of series and shunting condensers in the frequency-determining circuit of the local oscillater, by the proper adjustment of which a variable tuning condenser of the ordinary concentricplate type may be utilized to maintain a constant frequency difference between the local oscillation frequency and the frequency of the incoming signal.

The novel features that I consider characteristic of my invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its method of operation, together with further objects and additional advantages thereof, will best be understood by reference to the following description of a specific embodiment, taken with the accompanying drawings, in which:

Figure 1 is a schematic wiring diagram of a complete radio receiving system comprising a preferred embodiment of my invention;

Fig. 2 is a diagram illustrating the manner in which the various thermionic devices comprised in my improved radio receiving system are supplied with grid-biasing and anode-potentials ac cording to my invention;

Fig. 3 is a perspective view of one of the intermediate-frequency transformers, a portion of the shielding container thereof being broken away;

Fig. 4 is an end elevational view of the trans former shown in Fig. 3;

Fig. 5 is a top plan view of the coil-and-condenser-supporting element of the transformer assembly illustrated in Fig. 3;

Fig. 6 is a cross-sectional view taken along a line corresponding to the line VI--VI in Fig, 5;

Fig. 7 is a plan view of the under surface of the supporting element; and

Figs. 8 and 9 are modifications of the circuit of Fig. 2.

The radio receiving system illustrated in Fig. 1 comprises a thermionic coupling tube I, a radiofrequency amplifying tube 2, a first detector tube 3, a plurality of intermediate frequency-amplifying tubes 4 and 5, a second detector tube 6, an audio-frequehey-amplifying tube I, and an oscillator tube 8. All of the tubes, with the exception of the audio-frequency amplifier I, are of the equipotential cathode type illustrated in the patent to Nicolson, No. 1,459,412, and, each tube, excepting the said audio-frequency amplifier, is provided with a grid 9, an anode I0, an equipotential cathode II, and a heater-element I2. All of the heater elements I2 are connected in parallel, by means of a plurality of conductors I3 and I4, to the terminals of a secondary winding I5 of a power transformer I6, the primary winding ll of which may be energized from any convenient source of commercial-frequency alternating current.

The audio-frequency-amplifying tube 1 has a filamentary cathode I8 which is arranged to be energized by alternating current supplied from another secondary winding 20 of the power transformer over a plurality of conductors 2I and 22.

The thermionic cathodes II of the coupling tube I, the radio-frequency amplifying tube 2, and

those of the first and second intermediate-frequency-amplifying tubes 4 and 5, are connected together througha conductor 23 which terminates in an intermediate point 24 on a resistor 25, in order to fix their potential with respect to the grids of the several devices and the anodes thereof, in a manner hereinafter specifically described.

The cathode II of the first detector tube 3 is connected to the cathode II of the oscillator tube 8 over a circuit including a conductor 26 and a coupling-coil 21, the said cathodes, as well as the cathode of the second detector tube 6, being maintained at the same direct-current potential by a common connection 28 to one end of the resistor 25.

The coupling-coil 21 is positioned in inductive relation to an inductor 30 which is comprised in the frequency-determining input-circuit of the oscillator tube 8. A main tuning condenser 3I, a Vernier condenser 32 in shunt thereto, and a small variable condenser 33 are connected in shunt relation to the inductor 3D. The grid of the oscillator tube is variably connected to the inductor 30 through a grid condenser 34 and a stabilizing resistor 35, and a grid-leak 3'6 is provided to maintain the grid at the proper operating potential.

Anode-potential for the oscillator tube 8 is derived from the positive terminal of a rectifying device later to be described in more detail, the supply circuit including a feed-back inductor 31, positioned in inductive relation to the input inductor 30 which provides the necessary transfer of energy to maintain oscillations therein.

By reason of the inclusion of the inductor 21 in the connection between the cathode of the o oscillator tube and the cathode of the first detector tube, the local oscillation frequency is impressed on the first detector tube by causing the potential of its cathode to vary with respect to the potential of the grid, instead of causing the grid potential to vary with respect to the cathode, as is usual. The stability of the system seems to be improved to some extent by this method of connection.

The manner in which the small series adjusting condenser 33 and the shunt adjusting condenser 32 are included in the frequency-determining circuit of the oscillator is an important phase of my invention, since I am thereby enabled to so modify the capacity-displacement curve of the main tuning condenser 3I that a constant-frequency difference may be maintained between the tuning of the oscillator and the tuning of the radiofrequency stages of the amplifier without altering the shape of the oscillator tuning-condenser plates or without shifting the rotor thereof with respect to the stator.

The effective minimum capacity of the tuning condenser may be adjusted by the shunt condenser 32, while the maximum eifective capacity of the tuning condenser is determined by the ratio of the series condenser 33 to the total capacity of the tuning condenser and the shunt condenser. By properly adjusting the two added condensers, the curve expressing the relation between the total capacity effective to tune the frequency-determining circuit and the movement of the main tuning condenser may be made to quite closely approximate a predetermined shape. The great utility of the adjusting condensers 32 and 33 will be more apparent hereinafter.

The antenna-coupling tube I is provided with an input circuit comprising a resistor 33, one end of which is permanently connected to a grounded conductor 40 which terminates in a variable contact device M associated with the biasing-potential supply resistor 25. The other end of the input resistor 38 is provided with a connection whereby the said resistor may be included serially in an energy-collecting circuit including an antenna 42 and a ground connection 43. When the resistor 38 is included in the antenna-ground circuit, the antenna is rendered substantially incapable of radiating energy im- ISI) . denser 60.

parted thereto from the local oscillator, either through the Coupling tube or through the space outside of the container in which the entire receiving system is mounted.

A variable contact device 44 may be provided to permit the grid of the coupling-tube to be so connected to the input resistor that the signalvoltage applied to the tube may be altered at will to secure a measure of volume-control.

Signal-energy from the coupling tube l is applied to the input circuit of the radio-frequency amplifying tube 2 through a transformer 45, which is provided with a high-inductance primary constructed according to the disclosure in my copending application, Serial No. 151,722, filed November 30, 1926, which has issued as Patent No. 1,907,478 of May 9, 1933, and a secondary winding having a variable tuning condenser 46 connected in shunt thereto.

Regeneration in the amplifying tube is controlled through the agency of a feed-back circuit comprising an inductor 41 coupled to the secondary winding of the intertube transformer 45, andga small variable condenser 48 connected between the inductor 41 and the anode ll] of the amplifying tube.

The amplifying tube 2 is coupled to the first detector tube 3 through a transformer 50 having a high-inductance primary winding 5| and a secondary winding 52 shunted by a variable tuning condenser 53 and a fixed condenser 54 in series. The high-inductance primary winding 5| in the output circuit of the amplifying tube causes a certain amount of damping in the input circuit of the said tube, as explained in my aforementioned copending application, which accounts for the necessity of supplying the aforementioned feedback circuit to bring the amplification therein up to the proper value.

The first detector tube 3 is coup-led to the first intermediate-frequency amplifying tube 4 through a transformer 55 having a primary winding 56 shunted by a tuning condenser 51 and a secondary winding 58 shunted by a tuning con- Oscillation in the first intermediatefrequency amplifying tube is prevented according to the method disclosed in the patent to Rice, No. 1,334,118, a small condenser 6|, connected between the anode of the tube and the lower end of the secondary winding 58, being utilized to supply the proper anti-oscillation potentials.

The first intermediate-frequency-amplifying tube 4 is coupled to the second intermediate-frequency-amplifying tube 5 through a transformer 62, similar to that interposed between the first detector and the first intermediate-frequency amplifier, and the second intermediate-frequency-amplifying tube 5 is coupled to the second detector tube 6 through another analogous transformer 63. The three transformers 55, 62, and 63, being structurally alike, the several constituent parts of each have been similarly numbered in the drawings. Each transformer is totally enclosed by non-magnetic shielding material, indicated by the dotted rectangles, to minimize interaction between the several amplifying stages.

There is no tendency toward regeneration in the second detector 6, and, for that reason, the neutralizing condenser 61, which is a constituent part of the transformer-assembly 63, when manufactured, is not needed for netralizing, and it may, accordingly be connected in shunt relation to the tuning condenser 60, as shown.

The second detector tube 6 is coupled to the audio-frequency power-amplifying tube I through an audio-transformer T0 of any well known type, and the output circuit of the power amplifier may be coupled to a loud-speaker 'li through a blocking condenser 12, as illustrated, or through an output-transformer (not shown) The tuning condenser 46, comprised in the in put circuit of the radio-frequency amplifying tube 2, the tuning condenser 53 in the input circult of the first detector tube 3, and the tuning condenser 3| in the frequency-determining circuit of the oscillator tube 8, are all connected together, as indicated by the dotted lines 13, for simultaneous actuation, and the rotors thereof are connected to the grounded conductor 40.

In order to improve the selectivity of my receiving system, and to minimize the so-called image-frequency response, I have chosen an intermediate frequency of 180 kilocycles, and it is, accordingly, apparent that the frequency of the oscillator must always differ from the frequency of the desired signal by that amount. Manufacturing cost is leesened by giving the same contour to the rotor plates of all the tuning condensing, and by assembling the rotors of the tuning condensers on one shaft but, previous to my invention, this method of construction rendered it substantially impossible to so adjust the system, after assembly thereof into a completed set, that a constant frequency-difference could be maintained over the entire tuning range.

By providing the aforementioned adjusting condensers 32 and 33,'however, the effect of the tuning condenser 3| on the frequency of the oscillations generated by the oscillator may be so materially modified that the desired frequencydifference may be achieved, and maintained over the tuning range, without changing the value of the input inductor 30 or altering the position of the rotor of the oscillator-tuning condenser 31 with respect to the stator thereof, as was the procedure previous to my invention.

If the oscillator, instead of being tuned to a frequency higher than that of the incoming signal, is to be tuned to a lower frequency, the adjusting condensers 32 and 33 are associated with the input circuits of the radio-frequency amplifier tubes and the first detector tube, and not with the oscillator tube input circuit, as illus trated.

Anode potentials, grid-biasing potentials, and

cathode potentials for the various thermionic tubes are supplied from a rectifying device over a network which is arranged according to an important phase of my invention. The rectifying device 80 is of the full-wave rectifying type, having a plurality of anodes 8|. The device may be provided with a thermionic cathode 82, supplied with operating potential from a secondary winding 83 on the power transformer I6, or it may be of the cold-cathode type Which functions by virtue of gas-action, since the specific rectifier constitutes no part of my invention.

High potential for the anodes of the rectifying device is supplied from a secondary winding 84 on the power transformer, a connection 85 to an intermediate point on the said winding constituting the negative output-terminal of the rectifier. The positive output terminal of the rectifier, which is constituted by the cathode 82, is directly connected to the anode of the audio-frequency amplifier I, through a plurality of chokecoils 86, 81, and 88 and. a conductor 90. A plurality of by-pass condensers 9| and 92, of relatively large capacities, are connected in shunt to the rectifier output terminals, and provide, to-

tubes.

gether with the choke-coils, a filter circuit to exert a smoothing action on the rectified current.

Anode potential for the coupling tube I, the radio-frequency amplifying tube 2 and the intermediate-frequency amplifying tubes 4 and 5, is supplied from the positive terminal of the rectifier over a circuit including a resistor I00 and a common conductor IOI. Anode potential for the first detector tube 3 and the oscillator tube 8 is supplied from the positive terminal of the rectifier over a circuit including a conductor I02 and a resistor I03 of greater magnitude than the resistor I00, while anode potential for the second detector tube 6 is supplied from the positive terminal of the rectifier over a conductor I04.

In order that the manner in which the rectifier furnishes anode and grid-biasing potentials for the various thermionic devices may be more clearly understood, attention should also now be directed to Fig. 2 of the drawings in addition to Fig. 1. It will be noted that the positive terminal of the rectifier is directly connected to the anode of the audio-frequency amplifier tube 1, and to the anode of the second detector tube 6, thus supplying these tubes with maximum anode potential. Anode potential for the oscillator tube and the first detector are supplied over the resistor I03, one end of which is connected to the conductor 90.

The cathodes of the oscillator tube, the first detector tube, and the second detector tube are conductively connected, by the conductor 28, to an intermediate point on a resistor I05 arranged in shunt to the secondary winding 20, to an intermediate point on a resistor I06 arranged in shunt to the heater-winding I5 and to one end of the previously referred-to bias-potential resistor 25. The resistor 25 preferably comprises a plurality of fixed resistor elements I01 and I00 and a portion IIO with which is associated the movable contact device 4 I, one end of the portion I I0 being directly connected to the negative terminal 05 of the rectifying device.

The sum of the space currents in the oscillator tube, the first and second detector tubes and the audio-frequency amplifying tube, therefore, flows through the entire resistor 25, and causes a fall in potential thereacross, the end nearest the rectifier terminal being obviously the negative end. Since the cathodes of the tubes just referred to are all connected to the positive end of the resistor 25, the grids of the tubes may be given appropriate negative biasing potentials by connecting them to points along the resistorelemenl; I01, as illustrated. It is preferable, however, to so arrange the oscillator that its grid potential is fixed by the value of the grid condenser 34 and the grid-leak 36, instead of by a connection to the resistor I01.

The cathodes of the coupling tube, the radiofrequency amplifying tube and the two intermediate-frequency amplifying tubes are connected to a point on the resistor 25 intermediate the sections I01 and I08, and a resistor I20 is connected in shunt to the space-current paths of the said tubes. The fall in potential across the resistor sections I00 and H0 is accordingly in part fixed by the current flowing through the resistor I20, in part by the space-current in the highfrequency amplifying tubes I, 2, 4, and 5, and in part by the space-current in the remaining By choosing proper values for the resistor I20 and the resistor section I08, the potential of the contact-device 4I may be maintained highly negative, notwithstanding marked variation in the space currents from the several tubes.

The contact device 4| may, accordingly, be utilized to vary the magnitude of the negative potential applied to the grids of the high-frequency amplifying tubes I, 2, 4, and 5, for volume-control purposes while the system is in operation, with the full assurance that an ample negative potential is always available.

In some instances, particularly when my improved receiving system is operated relatively close to a powerful broadcasting station, it is necessary for complete volume-control, to provide means whereby the grid of the coupling tube I may be given a more negative bias than the grids of the succeeding amplifying tubes. This may be accomplished by providing a separate variable connection I13 from the cathode of the coupling tube to the resistor 25, whereby upon movement of the contact device III toward the negative end of the resistor element IIO, the said variable connection is caused to simultaneously move toward the positive end of the resistor. Another way in which I may accomplish the same result is to connect the shunting resistor I251 with the thermionic tubes I and 2 alone, and to supply the tubes 4 and 5 with anode potential across a separate resistor I15, at the same time retaining the remaining connections as illustrated in Fig. 2. The modified circuit is illustrated in Fig. 9.

In either event, the shunting resistor I20 has the very important function of preventing an undue increase in the plate potential applied to the high-frequency amplifying tubes when they I are so negatively biased as to diminish the space currents therein.

A bypass condenser I30 is connected in shunt to the resistor I20, in order that potential fluctuations impressed thereacross shall not be effective to interfere with the action of the later devices in the series.

A similar bypass condenser I3I is connected in shunt to the space-current paths of the oscillator and first detector tubes for an analogous purpose.

Additional bypass condensers I32, I33 and I34 are provided for the purpose of forming low impedance paths around the resistor assembly.

The variable contact device I I I, or volume control, is provided with a connection to ground, and to the chassis of the set, for safety purposes.

An important phase of my invention is con cerned in the construction and arrangement of the intermediate-frequency coupling transformers 55, B2 and 63, which are shown in detail in Figs. 3 to 7, inclusive, of the drawings, in order that the intermediate stages may have the requisite selectivity and yet not be so sharply tuned that the quality of the signals is impaired.

Each of the intermediate-frequency transformers comprises an insulating plate I40 which rests upon, and is supported by, two of the upper edges of a metallic shielding container MI. The container, which is preferably rectangular in form, is provided with a plurality of upwardlyextending ears I 42 adapted to be inserted upwardly through openings in a metallic frame element incorporated into the chassis of the set (not shown), and bent over to maintain the container firmly in position.

The primary winding 56 and the secondary winding 58 are coaxially mounted on an insulating form I50 which is suspended from the cover plate I40 by means of a plurality of angu- Iii) larly bent arms I5I. The coupling between the windings may be varied within the limits of the length of the form for a purpose hereinafter described more in detail.

The fixed primary tuning condenser 51 is mounted on the upper surface of the insulating plate and is fastened thereto in any desired mannor, the said condenser being connected across the terminals of the primary winding by means of a plurality of conductors I52 and I53.

In addition to the fixed tuning condenser, the variable secondary tuning-condenser and the variable neutralizing condenser 6| are also carried by the cover plate, being mounted on opposite sides thereof.

Referring specifically to Figs. 5, 6, and '1, the variable tuning condenser 6-8 comprises an immovable plate I54 held to the upper surface of the cover-plate I40 by a plurality of solid rivets I55, and a flexible element I56, one end of which is affixed to the cover-plate by means of a hollow rivet I51. The upper end of the hollow rivet extends through an opening in the bottom of a small cup I], thus holding the cup and the end of the flexible element firmly in contact.

The variable neutralizing condenser 6| comprises an immovable plate I6I held to the under surface of the cover-plate I45] by a plurality of solid rivets I62, and a flexible element I63, one end of which is affixed to the cover-plate by means of a hollow rivet I64 having an interior thread.

An adjusting screw I65 extends downward through the hollow rivet which holds the end of the upper movable plate I56 in position and cooperates with a nut I66 affixed to the free end of the lower flexible element I63 to provide adjusting means therefor.

A small cup I61, having an opening through the bottom thereof, is afiixed to the free end of the upper flexible element I56 by a hollow rivet I68 through which extends an adjusting screw I10 that engages the interiorly threaded surface of the rivet I64, thus holding the end of the lower flexible element in position. The upper movable element of the condenser 60 may, accordingly,

be adjusted with reference to the fixed plate thereof by rotating the said screw.

The terminals of the tuning condenser 60 and the neutralizing condenser 6! may be connected to lugs. I1I mounted on the edges of the cover plate, or to the proper terminals of the primary and secondary windings, as shown in Fig. i.

The small cups I60 and I61 are filled with sealing-wax, or an analogous material, after the condensers have been properly adjusted, which partially prevents subsequent tampering with the adjustment. Tampering with the condenser adjustment is still further prevented by the novel manner in which the shielding containers are mounted beneath the chassis of the set, as hereinbefore described.

When both the primary winding and the secondary winding of the transformer are properly tuned, and the coupling between the windings adjusted, it is found that the resonance curve thereof has a sufficiently wide peak to permit the efficient amplification of the side-band frequencies, a feature that is noticeably lacking in aircore intermediate-frequency transformers constructed previous to my invention.

Insofar as I am at present aware, it has not been previously suggested that economy of space and convenience in adjustment could be obtained by so mounting a plurality of variable condensers on the casing of an intermediate-frequency transformer that each of said condensers could be separately and independently adjusted from the exterior of the said casing. In addition, since the condensers are completely shielded electrically from other parts of the receiving system, when the container is mounted in place beneath the chassis, the opportunity for inter-circuit coupling, and consequent regeneration, is eliminated.

The space between the transformer windings and the inner walls of the shielding container is referably filled with an insulating compound, a mixture of beeswax and resin having been found very desirable for this purpose.

I have determined, by careful experiments, that, by utilizing my improved intermediate-frequency transformers in a superheterodyne receiving system, the amplification obtainable is greatly increased. Many factors enter into the improvement in amplification, the shortness of leads, the tuning of both primary and secondary, the complete shielding, and others which I have not, as yet, fully determined. Since the amplification, however, is improved, I am enabled to employ an intermediate frequency of the order of 180 kilocycles with good results, instead of the usual 40 kilocycle frequency, and the use of the high intermediate frequency very greatly reduces the image-frequency response of the system. By image-frequency response is meant the response of the system to an undesired signal which differs in frequency from the desired signal by twice the intermediate frequency. If, therefore, the intermediate frequency is high, the selectivity of the radio-frequency stages of the system will be such as to greatly reduce, in amplitude, any signal which differs from the desired signal by twice the said intermediate frequency.

It will, accordingly, be apparent that the several phases of my invention cooperate to enable the production of a superheterodyne receiving system that is superior, in many respects, to analogous receiving systems constructed according to the teachings of the prior art.

I am aware that many modifications of my invention may be suggested to persons skilled in the art, and that many other specific embodiments thereof are possible. My invention, therefore, is not to be limited except insofar as is necessitated by the prior art and by the spirit of the appended claims.

I claim as my invention:

1. A transformer comprising a tuned primary winding and a tunable secondary winding, an insulating support from which said windings are suspended, said support also serving to carry the tuning condenser for said windings, a variable condenser adapted for use as a neutralizing condenser, said variable condenser and one of said tuning condensers being afiixed to opposite sides of said insulating support and having a common terminal, and means accessible from one face of said support for adjusting said last mentioned condensers.

2. A transformer comprising a tuned primary winding and a tunable secondary winding, an insulating support from which said windings are suspended, said support also serving to carry the tuning condensers for said windings, a variable condenser adapted for use as a neutralizing condenser, said variable condenser and one of said tuning condensers being affixed to opposite sides of said insulating support and having a common terminal, means accessible from one side of said support for adjusting said last-mentioned condensers, and means whereby the adjustment of said condensers may be prevented from being easily disturbed.

3. Radio apparatus comprising a support, a member afiixed at one portion of its surface to one side of said support, means for altering the position of a free portion of said member, said means being accessible from the other side of said support, another member also affixed at one portion of its surface to the side of said support opposite that side to which the first member is aflixed, said means for altering the position of a tree portion of said first member, comprising also the means for affixing said second member to said support.

4. Radio apparatus comprising a plate, a plurality of condensers mounted on opposite sides of said plate, means for adjusting said condensers, said adjusting means being accessible from one side of said plate, the adjusting means for each condenser comprising means for mounting the other condenser on said plate.

5. A transformer coupling having a primary and secondary winding, one of said windings being tuned by a condenser, an insulating support from which said windings are supported, said support also serving to carry said condenser, said condenser comprising a pair of electrostatically spaced conductive members, one of said members being affixed at one portion of its surface to one side of said support and means for altering the position of a free portion of said member, said means being accessible from the other side of said support.

6. For use in an electric current amplifying system, having a plurality of tube devices for amplifying electric currents, an inductive coupling for coupling two of said tube devices comprising a coil and a variable condenser, a housing for said coil, a closure for said housing, said closure constituting the sole means for supporting both said coil and said condenser.

'7. A transformer coupling comprising a housing, a primary and secondary winding in said housing, one of said windings being tuned by a condenser, an insulating support from which said windings are suspended, a variable condenser adapted for use as a neutralizing condenser, said insulating support also serving to carry both said variable condenser and said tuning condenser, adjustable means for said condensers, said adjustable means being accessible from outside of said support.

8. For use in an electric current amplifying system in which a plurality of tube devices are employed for amplifying electric currents, a coupling for at least two of said tube devices, said coupling comprising a transformer having primary and secondary windings, one of said windings being tuned by a condenser, an insulating support from which said windings are supported, said support also serving to carry said condenser, a housing of metallic material for said windings, said insulating support resting on said housing to constitute a closure therefor.

9. In an amplifier system, a plurality of electric discharge devices having grid elements, means for impressing grid-biasing potentials on said grid elements, means for varying said potentials to compensate for variations in carrier intensity, the potential variations on certain of said grid elements which normally receive lower signal potentials than others, being greater than the variations on said other grid elements, whereby distortion on strong signals may be substantially eliminated.

10. In an amplifier system, a plurality of electric discharge devices having grid elements, means for impressing grid-biasing potentials on said grid elements, and means for altering said biasing potentials on certain of said grids normally receiving the least signal potetnials at a faster rate than on others of said grids.

11. In the operation, of a tube amplifier in cluding a plurality of stages for successively amplifying an incoming wave without change of frequency, the method of extending the range throughout which distortionless volume control may be effected which comprises progressively decreasing the range of control in successive stages of said amplifier.

12. The combination with a plurality of cascaded tube amplifier stages operating at the same frequency, of volume control means for effecting progressively smaller changes in the amplification of succeeding stages.

13. In a transmission system, the combination with a plurality of cascaded amplifier stages all amplifying received energy at the same frequency, of means associated with said stages for effecting a predetermined differential control of the amplification rates thereof in such a manner that the overall amplification is linear over the broadest permissible range.

14. An electrical transmission system of the type including a plurality of cascaded tube amplifier stages all amplifying received energy at the same frequency, and means for varying an energizing voltage of each stage to control overall amplification of said system, characterized by the fact that said amplification means includes elements progressively decreasing the range throughout which the energizing voltages of succeeding stages may be varied.

15. The combination with a plurality of cascaded amplifier stages for successively amplifying incoming energy at its received frequency, of means for varying an amplification-controlling voltage applied to each of said stages, and circuit elements in said voltage-variation means for progressively decreasing the voltage changes applied to successive stages.

16. In an amplifying system employing electron discharge devices in cascade, the method of controlling amplification which comprises varying the grid bias on a. plurality of said tubes and causing the change in amplification of the first of said tubes to occur at a greater rate during control than that of a tube following.

17. In a transmission system including cascaded tube stages, the method of securing a desired output level which comprises simultane ously varying the amplification of the several stages in inverse proportion to the signal amplitudes at the said stages.

18. In an amplifying system a plurality of amplifying devices in tandem, volume control means including resistance and a potential source for causing electric current to flow therethrough and means for including said resistance in varying amounts in the grid circuits of said amplifying devices the grid circuit of an earlier device including said resistance to a greater degree than subsequent devices, whereby the gain in said devices varies respectively in proportion to the degree of association of the several grid circuits with the resistor.

19. In an amplifying system, a plurality of amplifying devices connected in tandem, a grid circuit for each of said devices, a control circuit comprising a resistor and a source of potential for causing an electric current to flow therethrough to cause a drop of potential thereacross, means for variably including a portion of said resistor in the grid circuit of an earlier device in the system, means for variably including said resistor to a lesser extent in the grid circuit of a subsequent device and means for simultaneously varying, in the same sense, the amount of said resistor included in each of said grid circuits, whereby the gain in said devices is caused to vary respectively in proportion to the degree of association of the several grid circuits with the resistor.

20. In an amplifying system a plurality of amplifying devices in tandem, a control circuit comprising resistance and a potential source for causing electric current to flow therethrough, to cause a drop of potential thereacross and means for connecting said resistance in varying degrees with the grid circuits of said amplifying devices, an earlier device being associated in greater degree with said resistance than subsequent devices whereby a change in potential applied across said resistance Will produce unequal changes in potential applied to said grid circuits to thereby control the gain in said devices respectively in proportion to the degree of association of the several grid circuits with said resistance.

21. In the process of varying the amplification of cascaded radio frequency amplifier stages by impressing upon an element of each stage an adjustable control voltage the method which comprises progressively decreasing the range of control voltages impressed upon succeeding stages.

GEORGE L. BEERS. 

